Shielded delay line



INSERTlON Loss m DB INSERTION Loss m DB \NsERnoN Loss IN DB Ln-PQJ Aug.3, 1965 Filed Oct. 17, 1960 2 Sheets-Sheet 2 REFERENCE Y Mm. \NSERT\ONLoss MAX. lNSERTlON L055 FREQUENCY IN KM C,

REFERENQE FREQUENCY IN KMC REFERENCE] FREQUENCY. IN KMC fAMl-ZS E.HOLLAND 1 7 EARL M. POLZ/N INVENTORS United States Patent 3,199,054SIHELDED DELAY LINE ames E. Holland, Rolling Hills, and Earl M. Polzin,Palos Verdes Estates, Califi, assignors, by mesne assignments,

to Thompson Rama Wooldridge Inc., Cleveland, Ohio,

a corporation of Qhio Filed Oct. 17, 1960, Ser. No. 63,198 Claims. (Cl.333-31) This invention relates to electromagnetic energy transmissionapparatus and more particularly to energy Wave transmission devices inwhich interaction of a signal propagated therein between adjacentsections thereof is substantially eliminated and in which the insertionloss over the operating range of frequencies of the device may besubstantially equalized Where a wave transmission device which is notcompletely enclosed by a metallic boundary is placed in a configurationother than an isolated straight line, inlIBl'EICiiOIl of a signalpropagated therein with adjacently disposed sections thereof has longbeen a problem in the art. This interaction can, under manycircumstances, cause variations in the insertion loss of the Wavetransmission device. Where the wave transmission device is utilized as adelay line, it has been found that variations in the delay experiencedby .a signal that is propagated along the delay line will occur as aresult of the signal interaction between adjacently spaced sections ofthe delay line. One attempt which has been made to solve this problem istha of spacing the adjacent sections of the delay line so that thedistance between them is sufiicient to prevent interaction of the signalwhich is propagated along the line.

This problem of interaction of the signal in adjacent sections of a wavetransmission device becomes particularly acute when a transmission lineor the like is used as a delay line and is placed in the form of ahelix, spiral or the like, to obtain a maximum delay time within aminimum physical space. By using such a geometric configuration, theinteraction of the signal between adjacent turns of the wavetransmission device is diflicult to control. Heretofore, inteiturnspacing has been used in an attempt to solve the interaction problem.Although excellent results have been obtained in this manner, theresulting delay line is physically larger than is desirable and theweight thereof is increased beyond preferred limits. The relativelylarge size and weight is undesirable in many applications. Where soliddielectric material having conductors spaced thereon is used as thetransmission line, physical strength al o becomes quite an importantfactor, since, in some cases, the dielectric material which is utilizedis hard and brittle.

it is also well known in the prior art that, when using transmissiondevices such as the solid dielectric type above referred to, theinsertion loss of the device varies with the frequency. in manyapplications it becomes desirable to obtain a relatively constantinsertion loss over the frequency band of the particular apparatusirrespective of the signal frequency. For example, in some electronicsystems where a signal is to be delayed for a predetermined time beforeapplication to a sensing device, it is important that the delayed signalhave subtantially the same amplitude irrespective of frequency.

Accordingly, it is an object of the present invention to provide atransmission device in which interaction of the "Ice signal propagatedalong adjacently positioned sections thereof is substantiallyeliminated.

It is another object of the present invention to provide a transmissiondevice in which adjacent sections thereof may be spaced closer togetherthan has heretofore been possible in the prior art.

It is another object of the present invention to provide a transmissiondevice which may be used as a signal delay line and in which delayvariations as a result of the interaction of electromagnetic fields setup by the signal propagated along the delay line are substantiallyreduced.

It is another object of the present invention to provide a transmissiondevice which may be used as a delay line and in which the variation ininsertion loss is substantially reduced.

It is another object of the present invention to provide a transmissiondevice whichmay be used as a delay line and in which the voltagestanding wave ratio thereof is substantially reduced.

It is another object of the present invention to provide a transmissiondevice which may be used as a delay line and which is smaller and morerugged than delay lines heretofore known in the prior art.

It is another object of the present invention to provide a transmissiondevice which has a relatively constant insertion loss over itsoperational frequency band.

The novel features of the present invention are set forth in theappended claims. Further objects and advantages of the present inventionmay be ascertained from a reading of the following description taken inconjunction with the accompanying drawings which are presented by way ofexample only and are not intended as a limitation upon the scope of thepresent invention and in which:

FIGURE 1 is an illustration of a portion of one type of transmissiondevice which may be utilized in accordance with the present invention;

FIG. 2 is a side-elevational View, partly in cross section, of atransmission device in the form of a delay line in accordance with oneembodiment of the present invention;

FIG. 3 is a fragmentary view, partly in cross section, of a transmissiondevice in the form of a delay line in accordance with another embodimentof the present invention;

FIG. 4 is a side-elevational view, partly in cross section, of atransmission device in the form of a delay line in accordance with analternative embodiment of the present invention;

FIG. 5 is a graph illustrating insertion loss as compared to frequencyof a prior art delay line;

FIG. 6 is a graph illustrating insertion loss versus frequency of adelay line in accordance with one embodiment of the present invention;and

FIG. 7 is a graphillustrating insertion loss versus frequency of a delayline in accordance with another embodiment of the present invention.

In accordance with one aspect of the present invention, there isprovided a transmission device in the form of a wave guide whichincludes metallic conductors upon only a portion of the surface of thewave guide. The wave guide is arranged in a configuration such thatsections thereof are disposed adjacent other sections thereof. Metallicshielding means is disposed between adjacent sections of the wave guideto shield the adjacent sections from electromagnetic fields set up bythe signal propagated along 3 the wave guide while at the same time notinterfering with the signal which is propagated along the wave guide.

In accordance with another aspect of the present invention, anelectromagnetic energy absorbing material is disposed about an elongatedwave transmission device to maintain the insertion loss of the wavetransmission device substantially constant over the entire operatingfreuency range thereof.

In accordance with a specific embodiment of the present invention, thereis provided a wave guide comprising an elongated member of highdielectric constant material having metallic conductors spaced onopposed substan tially parallel surfaces thereof. The elongated memberis placed substantially in the form of a helix and is disposed within aplastic foam. Portions of the plastic foam are removed from betweenadjacent turns of the elongated helical member. The space which isthereby provided is filled with a material which provides shieldingbetween adjacent turns and which is capable of absorbing electromagneticenergy. ln this manner there is provided a wave guide which can operateas a delay line and in which the interaction between adjacent turnsthereof as a result of an electromagnetic energy wave propagatedtherealong is substantially eliminated and in which the insertion lossover the operating frequency range of the delay line remainssubstantially constant.

Referring now to the drawings and more particularly to FIG. 1 thereof,there is illustrated a transmission device such as a section of waveguide which may be utilized in accordance with the present invention.Although the following description of the present invention will begiven with reference to a Wave guide which consists of a high dielectricconstant material, such as titanium dioxide, having metallic conductorsaffixed to opposed substantially parallel surfaces thereof and which mayextend over the entire area of each of the opposed surfaces thereof, itshould be expressly understood that the present invention is applicableto any type of transmission device which is not completely surrounded bya metallic boundary.

As illustrated in FIG. 1, a transmission device which may be utilized inaccordance with the present invention includes an elongated member ofhigh dielectric constant material 11 having spaced on opposite surfacesthereof metallic electrically conductive layers 12 and 13. Thedielectric material 11 may be any known high dielectric constantmaterial within which electromagnetic energy waves may be propagated.Examples of such material are T efion, polystyrene, polyethylene, fiberglass, quartz, barium titanate, titanium dioxide or the like. Themetallic electrically conductive layers 12 and 13 which are applied tothe opposite surfaces of the dielectric material 11 may be any metalliccoating which is desired, but is preferably silver. The layers may beapplied by any means known to the prior art so that the layers arerelatively thin.

As is known to the prior art, a wave of electromagnetic energy which ispropagated within a transmission device such as that illustrated in FIG.1 extends outside the boundaries thereof to some degree depending uponthe dielectric constant of the material as compared to that of itsoperating atmosphere and the frequency of the energy wave. As the waveof energy is propagated along the transmission device, large electricfields are established at the uncoated boundaries of the high dielectricmate rial as a result of the difference between the dielectric constantof the material and of the atmosphere in which it is operating. However,the electric and magnetic fields extend beyond the boundaries of thedielectric material. The lower the frequency which may be propagatedalong the particular wave transmission device illustrated in FIG. 1, thegreater are the electric and magnetic fields which extend beyond theboundaries of the dielectric material. As the frequency increases, theelectric and magnetic fields are bound more and more within theboundaries of the dielectric material and between the metallic coatingsdisposed thereon. It is therefore apparent that if, in accordance withprior art teachings, a wave transmission device such as illustrated inFiG. l is placed in such a geometric configuration that various sectionsthereof are disposed adjacent each other, the adjacent sections must beso spaced as to prevent interaction between the electromagnetic fieldsextending beyond the boundaries thereof for the lowest frequency whichis to be generated within and propagated along the particular wavetransmission device.

Referring now more particularly to FIG. 2,' there is illustrated anelongated member of'a wave transmission device which has been placed inthe geometric configuration of a helix. Such a geometric configurationis particularly adaptable to such uses as a delay line, particularly atmicrowave frequencies. The helical configuration permits a greater delayper unit of physical length along the longitudinal axis of the helix. itis to be expressly understood, however, that any particular geometricconfiguration, such as a spiral, a sinuous shape, straight lines, or thelike, may be used in accordance with the teachings of the presentinvention.

As illustrated in FIG. 2, the helical delay line 2?; comprises aplurality of turns formed of an elongated striplike member of thecharacter illustrated in FIG. 1. As described heretofore, the dielectricstrip is metallized on both of the large area surfaces. The strip memberis edge-wound peripherally of an inner shield 25 so that the metallizedright-hand surface of one turn is disposed in facing relation to andspaced from the left-hand surface of the next adjacent turn. That is, inaccordance with the presently preferred embodiment, the strip member isedge-wound so that the metallic coated surfaces lie in planessubstantially normal to the longitudinal axis of the inner shieldcylinder 25. It should be expressly understood that the foregoingedge-wound arrangement is not essential to the present invention. It iscontemplated that the strip member might alternatively be fiat-wound sothat the metallic coated surfaces would be generally internal andexternal of the helix without departing from the scope of the invention.The helical delay line 21 of FIG. 2 is disposed within a container suchas a metal housing 22. Standard connectors 25) are provided forlaunching or generating a signal within and removing it from the helicaldelay line 21. Spaced from and disposed between adjacent turns of thehelical delay line 21 are shielding members 23. The shielding members 23prevent the electromagnetic field which is generated by the signal thatis propagated along the helical delay line 21 and which extends beyondthe boundaries thereof from interacting with the electromagnetic fieldwhich is present in an adjacent turn of the helical delay line. Tieshielding members may be constructed of any metal desired, butpreferably are silver or any low-loss material. in this manner, thespacing between adjacent turns of the helical delay line 21 may begreatly reduced from that which has heretofore been known in the priorart. The requirements for a shielding in accordance with the presentinvention are (1) that the shielding be spaced in such a manner as toprevent interaction of the electromagnetic field which is gen eratedwithin the Wave transmission device, and (2) that the shielding does notinterfere with the signal which is propagated along the transmissionline. It has been found that, when using a helical delay line asillustrated in FIG. Substantially all interaction of the electromagneticfield propagated along the adjacent turns of the delay line has beeneliminated.

The outer surface 24 of the-metal housing 22 may also be used as aportion of the shield as well as an inner member 25 which is insertedwithin the housing 22 and is substantially concentric with the outersurface 24. In this manner the helical delay line 21 is completelysurrounded by a shield. Such a shield not only prevents interaction ofthe signal in adjacent turns, but also prohibits any signals exterior tothe wave guide from interfering with the signal propagated therein.

As can be seen by reference to FIG. 5, in which insertion loss indecibels is plotted along the ordinate and frequency in kilomegacyclesis plotted along the abscissa for an unshielded prior art delay lineoperating over a frequency band of approximately two to fourkilornegacycles, the interaction of the signal between adjacent sectionsof the delay line produces an undesirable interference signal.

The insertion loss versus frequency of a delay line constructed inaccordance wifla the present invention as illustrated in FIG. 2 is shownin FIG. 6. It can readily be seen that substantially all of the signalinteraction has been eliminated and a smooth response is obtained overthe entire operating frequency band.

As above pointed out, as the frequency of a signal which is generatedwithin a delay line, such as illustrated in FIG. 1 or FIG. 2, isincreased, the electromagnetic field is maintained more and more withinthe boundaries of the high dielectric constant material. Since thisoccurs, the losses which the signal experiences as a result of beingpropagated along a particular wave transmission device increase as thefrequency increases, since the losses imparted to the signal by the highdielectric constant material are greater than that which the signalwould experience if it were propagated through air. As a result thereof,the insertion loss of a signal propagated along a delay line, asillustrated in FIG. 2, increases as the frequency increases. It issometimes desired that a signal which is propagated along a delay linehave a constant insertion loss irrespective of the frequency which isgenerated therein. When such a result is desired for any particularapplication, a material may be placed between adjacent turns of ahelical delay line, of the type illustrated in FIG. 2, which will absorbelectromagnetic energy which impinges thereon. In such a manner, theelectromagnetic energy extending beyond the transmission device at thelower frequencies is absorbed by the electromagnetic energy absorbingmaterial, hereinafter referred to as lossy material, whereas at thehigher frequencies less of the electromagnetic energy extends beyond thetransmission line and therefore is not affected by the lossy materialdisposed between adjacent turns.

The lossy material may be inserted in any manner desired between theturns, and, in accordance with a presently preferred embodiment of thepresent invention, the lossy material may be afixed directly to themetallic shielding members inserted between adjacent turns of the helix,as illustrated at 26 in FIG. 3. As is illustrated, there is provided ahelical delay line having a shielding member 23 disposed between each ofthe adjacent turns of the helical delay line, and the lossy material 26is disposed on opposite surfaces of each of the shielding members 23. Inthis manner, there is provided a helical delay line in accordance withthe present invention which provides a constant insertion lossirrespective of the frequency of the signal generated Within the delayline and which eliminates interaction between the electromagnetic fieldsgenerated as a result of the signal propagated along the delay line.

The lossy material 26 affixed to the opposite surfaces of the shieldingmembers 23 may be any carbon base compound, such as Aquadag, or may be ametallized plastic material, such as metallized fiber glass. The lossymaterial is applied in any manner desired so as to obtain very thincoatings on the order of a few thousandths of an inch thick. Forexample, the material may be sprayed or painted or may be affixed insheets.

Referring now more particularly to FIG. 4, there is illustrated analternative embodiment of a helical delay line in accordance with theteachings of the present invention. As is therein illustrated, acontainer 31 has disposed therein a helical delay line 32 which isconstructed of a wave guide similar to that illustrated in FIG. 1.Standard connectors 30 may be used for applying a signal to and removingit from the delay line 31. A plastic foam material 33 is disposed withinthe container 31 and completely surrounds the helical delay line 32.Portions of the plastic foam 33 are removed from between adjacent turnsof the helical delay line 32 to provide recesses 34 therein. A materialis then inserted within the open portions of the plastic foam 33, asillustrated at 35. This material operates to perform the functions ofboth shielding and absorbing the electromagnetic energy which isradiated from the adjacent turns of the helical delay line 32. Oneexample of a material which performs the dual function as abovedescribed is a mixture of silver paint and a carbon base material.

A delay line constructed in accordance with the configurationsillustrated in either FIG. 3 or FIG. 4 not only provides theelectrically desired operation as above described, but as well providesa substantially mechanically stronger apparatus than has heretofore beenknown in the prior art. For example, the shielding members 23 asillustrated in FIG. 2 provide rigidity to the wave guide device, and theplastic foam provides a shock absorbing material. Therefore, even if thehelical delay line were constructed of exceedingly brittle material, theplastic foam would tend to absorb whatever shocks may be imparted to thecontainer having the delay line mounted therein.

Referring 'now more particularly to FIG. 7, there is shown a graph ofinsertion loss versus frequency when using a delay line similar to thatillustrated in FIG. 3.

As can be seen from a comparison of FIGS. 6 and 7, the response of theshielded delay line in accordance with this embodiment of the presentinvention displays a relatively constant insertion loss over the entireoperating frequency band. 7

There has thus been disclosed a wave transmission device in whichinteraction between adjacent sections of such a device as a result ofthe electromagnetic energy radiated therefrom is substantiallyeliminated, and also in which there may be a constant insertion lossover the operating range of frequencies irrespective of variation ofsuch operating frequency.

What is claimed is:

1. A device for receiving and transmitting waves of electromagneticenergy, comprising: an elongated member, formed of a material having adielectric constant substantially higher than air, and having anelectrically conductive layer on opposed surfaces thereof and having aconvoluted form such that at least first and second portions of saidmember are disposed in side-by-Side adjacency; means for launching anelectromagnetic energy wave within said elongated member affixed to atleast one end thereof; shielding means disposed between said first andsecond portions; and a material for absorbing electromagnetic energyradiated from said elongated member disposed upon at least a portion ofthe surface of said shielding means adjacent said elongated member.

2. A device for receiving and delaying waves of electromagnetic energy,comprising: an elongated member, formed of a material having adielectric constant substantially higher than air, and having anelectrically conductive layer on opposed surfaces thereof and having -asubstantially helical form; means for launching an electromagneticenergy wave within said helically formed member afiixed to at least oneend thereof; .a metallic container for said helically formed member,said container having an outer portion completely surrounding theexterior of said helically formed member, said container'having acentral portion disposed internally of said helically formed member; anda substantially planar metallic member having a substantially helicalconfiguration disposed between adjacent turns of said helically formedmember and extending between the outer and inner portions of saidcontainer whereby each turn of said helically formed member iscompletely surrounded by a metallic shield.

3. A device for receiving and delaying waves of electromagnetic energy,comprising: an elongated member, formed of a material having adielectric constant substantially higher than air, and having anelectrically conductive layer on opposed surfaces thereof and having asubstantially helical form; means for launching an electromagneticenergy wave within said helically formed member aflixed to at least oneend thereof; a metallic container for said helically formed member, saidcontainer having an outer portion completely surrounding the exterior ofsaid helically formed member, said container having a central portiondisposed internally of said helically formed member; a substantiallyplanar metallic member having a substantially helical configuration disposed between adjacent turns of said helically formed member andextending between the outer and inner portions of said container,whereby each turn of said helically formed member is completelysurrounded by a metallic shield; and a material for absorbingelectromagnetic energy radiated from said helically formed memberdisposed upon at least a portion of the surface of said metallic memberadjacent said helically formed member.

4. A device for receiving and transmitting waves of electromagneticenergy, comprising: an elongated member, formed of a material having adielectric constant substantially higher than air, and having anelectrically conductive layer on opposed surfaces thereof and having aconvoluted form such that at least first and second portions of saidmember are disposed in side-by-side adjacency; means for launching anelectromagnetic energy wave within said elongated member affixed to atleast one end thereof; a metallic container disposed about andcompletely surrounding said elongated member; a shock absorbing materialwithin said container and contacting said elongated member; andshielding means within said container and disposed extending betweensaid portions, said shock absorbing material being disposed between saidelongated member and said shielding means.

5. A device for receiving and transmitting waves of electromagneticenergy, comprising: an elongated member, formed of a material having adielectric constant substantially higher than air, and having anelectrically conductive layer on opposed surfaces thereof and having aconvoluted form such that at least first and second portions of saidmember are disposed in side-by-side adacency; means for launching anelectromagnetic energy wave within said elongated member affixed to atleast one end thereof; a metallic container disposed about andcompletely surrounding said elongated member; a shock absorbing materialwithin said container and contacting said elongated member; shieldingmeans within said container and extending between said portions, saidshock absorbmg material being disposed between said elongated member andsaid shielding means; and a material for absorbing electromagneticenergy radiated from said elongated member disposed upon at least aportion of the surface of said shielding means adjacent said elongatedmember.

6. A device for receiving and delaying waves of electromagnetic energy,comprising: an elongated member, formed of a material having adielectric constant substantially higher than air, and having anelectrically conductive layer on opposed surfaces thereof and having asubstantially helical form; means for launching an eletromagnetic energywave with said elongated member afiixed to at least one end thereof; ametallic container disposed about and completely surrounding saidelongated member; a shock absorbing material within said container andcontacting said elongated member; and shielding means disposed betweenadjacent turns of said elongated member to thereby substantially preventinteraction of the signal propagated along adjacent turns of saidelongated member.

7. A device for receiving and delaying waves of elec- 8 tromagneticenergy, comprising: an elongated member, formed of a material having adielectric constant substantially higher than air, and having anelectrically conductive layer on opposed surfaces thereof and having asubstantially helical form; means for launching an eletromagnetic energywave with said elongated member affixed to at least one end thereof; ametallic container disposed about and completely surrounding saidhelically formed member, said container having an outer portion and aninner portion each extending longitudinally of said helically formedmember and spaced from the outer and inner surfaces thereofrespectively; a shock absorbing material surrounding said helicallyformed member and disposed within the inner and outer portions of saidcontainer; and shielding means disposed between adjacent turns of saidhelically formed member and through said shock absorbing material.

3. A device for receiving and delaying waves of electromagnetic energy,comprising: an elongated member, formed of a material having adielectric constant substantially higher than air, and having anelectrically conductive layer on opposed surfaces thereof and having asubstantially helical form; means for launching an electromagneticenergy wave within said member affixed to at least one end thereof; ametallic container disposed about and completely surrounding saidmember, said container having an outer portion and an inner portion eachextending longitudinally of said member and spaced from the outer andinner surfaces thereof respectively; a shock absorbing materialsurrounding said member and disposed within the inner and outer portionsof said container; and shielding means disposed between adjacent turnsof said member and through said shock absorbing material, said shieldingmeans including means for absorbing electromagnetic energy radiated bysaid member.

9. A device for receiving and delaying waves of electromagnetic energy,comprisin an elongated member, formed of a material having a dielectricconstant substantially higher than air, and having an electricallyconductive layer on opposed surfaces thereof and having a substantiallyhelical form; means for launching an electromagnetic energy wave withinsaid member affixed to at least one end thereof; a metallic containerdisposed about and completely surroundingsaid member, Said containerhaving an outer portion and an inner portion each extendinglongitudinally of said member and spaced from the outer and innersurfaces thereof respectively; a shock absorbing material surroundingsaid member and disposed within the inner and outer portions of saidcontainer, said shock absorbing material substantially filling the spacebetween said outer and inner portions and defining openings betweenadjacent turns of said member; and metallic shielding means disposedwithin said openings for inhibiting interaction of electromagnetic waveswhich may extend from said adjacent turns.

lit. A device for receiving and delaying waves of electromagneticenergy, comprising: an elongated member, formed of a material having adielectric constant substantially higher than air, and having anelectrically conductive layer on opposed surfaces thereof and having asubstantially helical form; means for launching an electromagneticenergy wave within said member affixed to at least one end thereof; ametallic container disposed about and completely surrounding saidmember, said container having an outer portion and an inner portion eachextending longitudinally of said member and spaced from the outer andinner surfaces thereof respectively; a shock absorbing materialsurrounding said member and disposed within the inner and outer portionsof said container, said shock absorbing material substantially fillingthe space betwen said outer and inner portions and defining openingsbetween adjacent turns of said member; a mixture of silver and a carbonbase compound substantially filling each of said openings whereby eachturn of said member is shielded from adjacent turns thereof ande'lectrornagneiic energy radiated from said member is absorbed.

References Cited by the Examiner UNITED STATES PATENTS De Rosa 333-31Rumsey et a1. 33384 Tiley 333-31 Hebenstreit 33331 Grieg et a1. 333-8410 Adams 333--84 Fox 33395 X Sabaroff 333-79 Arditi 33384 Lovick.

Lewis 333 -31 Germain 33379 Barrett 333-79 HERMAN KARL SAALBACK, PrimaryExaminer.

E. JAMES SAX, Examiner.

1. A DEVICE FOR RECEIVING AND TRANSMITTING WAVES OF ELECTROMAGNETICENERGY, COMPRISING: AN ELONGATED MEMBER, FORMED OF A MATERIAL HAVING ADIELECTRIC CONSTANT SUBSTANTIALLY HIGHER THAN AIR, AND HAVING ANELECTRICALLY CONDUCTIVE LAYER ON OPPOSED SURFACES THEREOF AND HAVING ACONVOLUTED FORM SUCH THAT AT LEAST FIRST AND SECOND PORTIONS OF SAIDMEMBER ARE DISPOSED IN SIDE-BY-SIDE ADJACENCY; MEANS FOR LAUNCHING ANELECTROMAGNETIC ENERGY WAVE WITHIN SAID ELONGATED MEMBER AFFIXEAD TO ATLEAST ONE END THEREOF; SHIELDING MEANS DISPOSED BETWEEN SAID FIRST ANDSECOND PORTIONS; AND A MATERIAL FOR ABSORBING ELECTROMAGNETIC ENERGYRADIATED FROM SAID ELONGATED MEMBER DISPOSED UPON AT LEAST A PORTION OFTHE SURFACE OF SAID SHIELDING MEANS ADJACENT SAID ELONGATED MEMBER.